There are generally four types of known methods followed to form sockets on the ends of polyolefinic material tubes for pressurised fluids.
According to a first method, the tube is manufactured in an injection moulding process which allows the socket forming of its end.
According to another of the known methods mentioned above, the end of the tube is defined by a tubular union, which is firstly socket-formed in an injection moulding process and is then head-welded to the tube normally made by extrusion.
Evidently, the first two methods of the known type described above present some drawbacks mainly deriving from the fact that such methods are relatively complex and costly, requiring relatively long actuation times and not being suitable to be used in an automatic tube manufacturing line.
According to the third of the abovementioned known methods, the end of the tube is firstly heated and then formed by forcing the polyolefinic material against a shaped mould external to the tube by means of compressed air fed inside the tube, and is finally further formed by forcing the polyolefinic material against a shaped mould inside the tube by means of compressed air fed against the outer surface of the tube itself. Such method presents some drawbacks mainly deriving from the fact that the two forming steps described above require relatively high deformation forces and times.
According to the last of the abovementioned known methods, the end of the tube is firstly heated, then formed by forcing the polyolefinic material against a shaped mould external to the tube by means of compressed air fed inside the tube, then cooled, and finally mechanically compressed by means of two mobile jaws so as to obtain the final dimensions of the socket end by combining the compression action of the mobile jaws with the elastic behaviour of the polyolefinic material. The latter method requires relatively high deformation forces and times, is essentially incapable of ensuring a correct value of the thickness of the socket end and therefore entails a final step of monitoring the thickness of the socket end itself.